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Research Articles: Therapeutics, Targets, and Development

In vivo silencing of a molecular target by short interfering RNA electroporation: tumor vascularization correlates to delivery efficiency

Departments of ¹ Biochemistry and ² Clinical Immunology of Internal Medicine, Nagoya University Graduate School of Medicine; ³ Kinoe Co., Ltd., Nagoya, Japan and ⁴ Nepa Gene Co., Ltd., Chiba, Japan

Requests for reprints: Yoshifumi Takei, Department of Biochemistry, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan. Phone: 81-52-744-2064; Fax: 81-52-744-2065. E-mail: takei{at}med.nagoya-u.ac.jp

Abstract

Screening for a molecular target for cancer therapy requires multiple steps, of which an important one is evaluation of the knockdown effect of the target molecule on pregrown xenograft tumors. However, methods currently used for local administration of knockdown reagents, such as short interfering RNA (siRNA), are not satisfactory as to simplicity and efficiency. We established an electroporation method involving a constant voltage and "plate and fork" type electrodes and used it for in vivo delivery of siRNA. The delivery efficiency correlated to the electric current. The electric current correlated to the microvascular density and vascular endothelial growth factor (VEGF) expression and exhibited a threshold that guaranteed efficient delivery. Consequently, we showed that the vascularization and VEGF expression in tumors determined the efficiency of delivery of siRNA by electroporation. VEGF was chosen as a model target. VEGF siRNA electroporation suppressed the growth of tumors exhibiting high VEGF expression to less than 10% of the control level, but it had no effect on low VEGF-expressing tumors. Notably, a long interval (20 days) of electroporation was enough to obtain a satisfactory effect. Systemically injected siRNA could also be delivered into tumors by this method. Our data will provide the technical basis for in vivo electroporation, and this simple and efficient siRNA delivery method is applicable to in vivo comprehensive screening for a molecular target. [Mol Cancer Ther 2008;7(1):211–21]

Grant support: Ministry of Education, Science, Sports and Culture of Japan grants-in-aid 17016030, 10CE2006, and 21th COE grant and Japan Society for the Promotion of Science grants 15390103, 17790185, and 19590273.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

⁵ Supplementary materials for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

⁶ Y. Hayakawa, unpublished results.

⁷ Y. Takei, unpublished results.

Received 5/ 8/07; revised 10/28/07; accepted 11/28/07.